Device for selectively separating particles in a liquid, in particular for cleaning fibrous paper suspensing

ABSTRACT

A device for separating particles in a liquid in which a paper suspension  to be cleaned and supplied to a chamber of revolution (1) rotating about an axis (2). Movable deviators (7, 8) precede the fixed outlets (9, 10) to intercept most of the through-put of the suspension in the region of the periphery of the chamber (1), then deviate it towards the longitudinal axis of rotation (2) so as to recover most of the kinetic energy of rotation. The outlets (7, 8, 9, 10) are situated at the opposite end to that of chamber (1) from the supply (5, 6) and are arranged at the periphery of this chamber (1). A diabolo-shaped central body of revolution (11) is arranged inside the chamber, along the longitudinal axis of rotation (2) for rotation about its axis and with a radial run-off (12) in the vicinity of its smallest cross-section connected to an axial outlet duct (13).

FIELD OF THE INVENTION

The invention relates to a device for selectively separating particlesin a liquid, in particular in a suspension. The invention isparticularly suitable for the paper industry, in particular the cleaningof particulate suspensions, for example fibrous suspensions. Theinvention may, however, find other applications in separation orcentrifugal fractioning techniques, in the recovery of immiscibleliquids of differing densities, etc.

BACKGROUND OF THE INVENTION

There currently exists in the paper industry a large number ofapparatuses intended for the cleaning or separation of fibroussuspensions.

In the document EP-B-0,037,347 of the Applicant (corresponding to U.S.Pat. No. 4,443,331), a free vortex device has been proposed, in whichthe suspension to be cleaned is supplied to a chamber of revolutionrotating about its axis, of the type comprising:

fixed means for supplying the suspension, arranged along thelongitudinal axis of said chamber of revolution, extended by movablemeans for deviating the suspension current towards the periphery of thechamber;

means for driving said chamber in rotation about its longitudinal axis;

fixed means for discharging the cleaned suspension and various separatedfractions, arranged along the longitudinal axis of said chamber,preceded by movable deviating means and in which the means fordischarging the lightest components is arranged along the longitudinalaxis of rotation (2) on the same side as the supply means,

wherein:

the movable deviating means preceding the fixed outlet means interceptmost of the throughput of the suspension in the region of the peripheryof the chamber, then deviate it towards the longitudinal axis ofrotation, so as to recover most of the kinetic energy of rotation;

and wherein the main outlet means are situated at the opposite end tothat of the chamber comprising the supply means and are arranged at theperiphery of this chamber, so that a large central centrifugal zone isavailable.

This device provides excellent results as regards efficiency, rejectrate and energy consumption, in particular for outputs less than aboutthree hundred cubic meters per hour of diluted pulp (concentration ofthe order of 1%). In order to treat effectively higher outputs, i.e.throughputs greater than 300 cubic meters per hour of diluted pulp, itbecomes necessary to increase the volume of the apparatus and hence itsdiameter. These large apparatus with a high cleaning capacity thus havevarious drawbacks depending on the conditions of their use.

Thus, if diluted pulp is being treated, there is first of all anincrease in the pressure drop in the region of the bearings and theinlet/outlet ends, as well as in the peripheral cleaning zone, onaccount of the need to maintain sufficient turbulence with a highthroughput. Furthermore, again in the case of diluted pulp, it becomesnecessary, on account of the larger diameter, to increase thecounterpressure at the outlet in order to extract the rejectsintercepted along the axis of the central zone of the vortex, oralternatively to intercept it at the periphery of this zone: there isthus formed along the axis of the apparatus an air core which, having nofixed geometry, moves inside the suspension and generates vibrationsthroughout the body of the apparatus.

If treating pulp with a higher concentration (up to about (3)% (sic),the problems which arise are different. First of all, owing to thecentrifugal force effect, the pulp tends to accumulate against thewalls, thus also resulting in the risks of vibrations due to imbalancesand clogging of the apparatus by very concentrated pulp. Furthermore, inorder to individualize the movement of the fibers, it is necessary tomaintain a high degree of turbulence and, for this reason, a bigdifference in peripheral/wall flow speeds, thus resulting in highpressure losses. Moreover, control of the flow at the periphery of thevortex, by the geometry of the ends, and that of the body of theapparatus essentially for small diameters, is fairly delicate and posesproblems as regards homogeneity of flow, which may adversely affect thequality of cleaning and which result in the risk of deposits.

SUMMARY OF THE INVENTION

The present invention overcomes these drawbacks.

It relates to an improved device of the same type as that described inthe document EP-B-0,037,347, in which control of the flow in theperipheral cleaning zone is improved and evacuation of the light rejectin the central zone of the vortex is promoted, even in the case of highthroughputs, while ensuring stable operation of the apparatus.

The subject of the invention is also an improved device of the type inquestion enabling large quantities of pulps of the order of five hundredmeters cubed per hour (500 m³ /h) and more to be cleaned.

This improved device for separating particles in a liquid, in which thesuspension to be cleaned is supplied to a chamber of revolution rotatingabout a longitudinal axis, of the type comprising:

fixed means for supplying the suspension, arranged along thelongitudinal axis of the chamber of revolution, extended by movablemeans for deviating the suspension current towards the periphery of thechamber;

means for driving said chamber in rotation about its longitudinal axis;

fixed means for discharging the cleaned suspension and the differentseparated fractions, arranged along the longitudinal axis of saidchamber, preceded by movable deviating means and in which the means fordischarging the lightest components is arranged on the longitudinal axisof rotation, either on the side where the suspension to be cleaned isadmitted or on the side where the cleaned suspension is discharged, andin which:

the movable deviating means preceding the fixed outlet means interceptmost of the throughput of the suspension in the region of the peripheryof the chamber, then deviate it towards the longitudinal axis ofrotation so as to recover most of the kinetic energy of rotation;

the outlet means are situated at the opposite end to that of the chambercomprising the supply means and are arranged at the periphery of thischamber;

wherein moreover a central body of revolution is arranged inside thischamber along the longitudinal axis of rotation of the chamber, betweenthe means supplying the suspension and the means discharging the cleanedsuspension, the said central body of revolution:

having a general convergent shape from the inlet means towards theoutlet means;

and comprising a run-off means arranged in the vicinity of the smallestcross-section of said central body of revolution, connected to an axialoutlet duct.

In other words, the invention consists in providing in the devicedescribed in the document EP-B-0,037,347 of the Applicant, a singlerigid central body with a general tapered and convergent shape insidethe chamber, which occupies the decreasing part of the gap between thesupply and outlet means, associated with a run-off means arranged in thevicinity of its smallest cross-section and intended to extract the lightfraction of the suspension.

The run-off system provided in the central body of revolution of theapparatus converts the residual energy of the vortex (dynamic and staticpressures) into static pressure. This avoids the counterpressure on theoutlet side and therefore enables the inlet pressure to becorrespondingly reduced, resulting in an appreciable saving in energy.

Advantageously:

the gap between the inner wall of the chamber and the wall of thecentral body increases gradually from the inlet towards the outlet;

the chamber has an inner cylindrical general shape and thecharacteristic central body has a diabolo shape;

the diabolo-shaped central body comprises three distinct portions,namely:

a first frustoconical portion, tapered towards the outlet;

a second cylindrical portion connected to the first portion, having atits periphery orifices associated with the run-off means;

a third portion, also frustoconical, but with a conicity which isopposite to that of the first portion, connected to the secondcylindrical portion and having an axial duct associated with the run-offmeans and intended to extract the light fraction;

the run-off means consist of radial fins associated with the peripheralorifices of the second cylindrical portion;

the inlet and outlet ends of the central body are integral with thechamber of revolution and are driven in rotation by a single motor atthe same speed as the speed of rotation of said chamber;

the central body is driven in rotation at a speed which is differentfrom that of the chamber, but is integral with the inlet and/or outletends of the chamber; in this case, the central body advantageously hasfins at the periphery, arranged along a generatrix.

In the sector of centrifuges, or centrifugal settlers, it has been knownfor a long time to arrange, inside the rotor, a central bodysubstantially of revolution and with a shape similar to the generalinner shape of the rotor. This shape defines a flow space with asubstantially constant thickness so as to avoid any unfavorableagitation during the settling of the suspension. This central bodygenerally has scraping or run-off elements for the heavy particles whichhave settled against the inner wall of the rotor so as to return them tothe vicinity of the axis and to extract them from the apparatus (see,for example, FR-A-1,450,895 (corresponding to U.S. Pat. No. 3,467,304);U.S. Pat No. 4,332,350 or GB-A-1,366,170). On the other hand, in thedevice of the invention, the central body of necessity has a shape whichis different from the inner wall of the chamber, in particular at thelevel of the run-off devices, so as to return to the vicinity of thecentral body, and to extract in the axis, not only the heavy particles,but also the light fraction of the suspension.

Thus, for the extraction of the light fractions, the state of the artargued against the use of a central body.

In other words, the invention consists, for this new application and inorder to obtain the objective of extracting the light fraction, indefining a particular and specific shape for the central body relativeto the inner wall of the chamber, namely a convergent shape, and inpositioning the run-off point on this central body at the point with thesmallest cross-section.

If the central body is integral with the rotating chamber of theapparatus, the apparatus is in this case particularly suitable for thesector of fine cleaning into diluted pulp, since the presence of thecentral body allows the flow to be channeled more effectively, inparticular upon leaving the injection channels of the inlet end. Infact, the parasitic recirculation currents as well as the radialvariations in angular speed of the pulp are reduced, thereby making theflow more uniform, in particular with a more homogeneous turbulentcondition.

On the other hand, if the central body is driven in rotation separatelyfrom the rotating body of the apparatus, but integrally with thesuspension inlet and/or outlet end(s), the apparatus is thus perfectlysuited to the cleaning of more concentrated suspensions. In fact,control of the flow in the external peripheral zone is improved not onlyby the presence of the central body but also by the choice of itsrotational speed differential, which enables the pulp to be entrained inrotation again, so that the suspension retains an optimum degree ofturbulence. In practice, the rotational speed differential of thecentral body is chosen according to the difference in speed of thesuspension relative to the wall in the region of the injection zone,depending on the characteristics of the supply end.

The chamber, the supply means, the movable deviating means, the outletmeans and the rotational driving means are made in a known manner,notably in accordance with the teachings of the document EP-B-0,037,347referred to in the preamble, for example from stainless steel.

The convergent central body has the following characteristics:

a conical (diabolo) shape converging from the suspension supply andoutlet ends enables the light reject to be properly evacuated, bypromoting the displacement of the light components towards theextraction zone which may be situated at any level between the ends, andin particular towards the outlet end, where the latter comprises theaxial tube for evacuation of the light reject;

the diameter of the run-off, arranged at the point of the diabolo withthe smallest cross-section, must be sufficiently great in order to avoidthe formation of the air core and in order to recover the residualpressure necessary for the extraction of the light fraction, but it mustalso be substantially less than the internal diameter of the chamber inorder to avoid the simultaneous extraction of heavy particles;

the diameter of the central body in the region of the supply and outletends must be fairly large in order to control properly the flow in theperipheral cleaning zone, and more particularly in the region of thesupply end, so as to channel the parasitic currents more effectively; inthe case where the central body is driven in rotation separately fromthe body of the apparatus, this central body may advantageously beequipped with elements for re-entrainment of the suspension, such asradial fins arranged longitudinally on its surface and more or lessclose to the wall according to the shearing, and hence the turbulencerequired.

For technical and mechanical reasons, the inner wall of the chamber iscylindrical. A slightly frustoconical general shape could, if required,be used with the proviso that, as already stated, the distance betweenthe walls of the chamber and of the central body increases uniformlyfrom the inlet towards the run-off device. This slightly frustoconicalarrangement entails, however, an increased construction cost which isnot essential.

The manner in which the invention may be achieved and the advantagesarising therefrom will emerge more clearly from the examples ofembodiment taken in conjunction with the attached figures.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows in basic schematic form, in longitudinal cross-section, anapparatus in which the characteristic central body is integral with thechamber of the apparatus.

FIG. 2 shows in schematic form, in longitudinal cross-section, anapparatus where the central body is capable of being driven in rotationseparately from the chamber of the apparatus.

FIG. 3 shows in basic schematic form, in longitudinal cross-section, apreferred embodiment of the invention, whereas FIG. 4 illustrates, incross-section, a detail of FIG. 3 (run-off) taken along the axisIV--IV'.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, the cleaning apparatus consists of:

an internally and externally cylindrical hollow chamber (1) driven inrotation about its longitudinal axis (2), by known means, not shown(motor);

bearings (3) and (4), associated with conventional seals (20-24),allowing the chamber (1) to rotate about its axis (2);

a tube (5) forming a fixed means for supplying the suspension to becleaned and leading by means of a connection piece rotating at the endof the chamber (1) into a supply duct (6) forming a movable deviatingmeans;

opposite the inlet means (5,6) and opposite the assembly (1), outletmeans also formed by two fixed ducts (9,10) forming fixed outlet means,connected via rotating connection pieces, respectively to the duct (7)closest to the outlet periphery, for the extraction of the heaviestparticles and to the concentric outlet duct (8), for the extraction ofthe intermediate fraction;

a diabolo-shaped rigid characteristic central body of revolution (11)aligned on the longitudinal axis (2) and fixed to the chamber (1) bysealed means (not shown); this central body (11) comprises a radialrun-off or radial passage means (12) (having an inlet remote from theaxis of the chamber 1) situated in the smallest cross-section of thediabolo and open to the chamber to collect the lightest fraction of thesuspension closest to the axis of rotation (2); consequently, thedistance D (FIG. 3) between the inner cylindrical wall of the chamber(1) and the wall (51) of the diabolo (11,30) increases uniformly fromthe inlet (5,6) towards the outlet (7,8);

an outlet duct (13) for the cleaned suspension, open to the radial innerend of the run-off (12) and along the longitudinal axis (2) of thechamber (1), for eliminating the lightest fraction of the suspensioncollected by the run-off (12).

This therefore constitutes an improved cleaner of the type described inthe aforementioned document EP-B-0,037,347, having a cylindrical chamber(1) in which is arranged a diabolo-shaped single central body (11) witha run-off (12) in the smallest cross-section, which promotes the removalof light reject, reduces the pressures necessary for effective operationof the cleaner, avoids vibration problems and improves the homogeneityof the suspension.

On the device of FIG. 2 the central body (11) and the inlet (6) andoutlet (7) means form an integral unit driven in rotation separatelyfrom the chamber. As in FIG. 1, the fixed means (5) and (8) areconnected to the movable means (6) and (10) respectively by sealedconnections (20-24) and the central body has a diabolo shape that, twooppositely directed cones joined at their smallest diameter ends. Thisdiabolo (11) is also equipped at the periphery with fins (14,15) forentraining the suspension to be cleaned, arranged along generatrices andequidistant from each other. Bearings (16,17) associated withconventional seals (23,24), allow the central diabolo (11) to rotateabout the longitudinal axis (2) at an appropriate speed. The run-off(12) provided in the central body forms a movable means for dischargingthe light fraction and is extended downstream by an evacuation duct (13)arranged along the axis (2). A radial run-off or radial passage means(18) provided in the outlet end (19) allows extraction of the heaviestfraction in the peripheral zone (7), forming the movable means fordischarging this heavy fraction. This run-off (18) is extendeddownstream by an outlet duct (25) arranged along the longitudinal axis(2). Movable means (26) for supplying an auxiliary dilution fluid areprovided along the outlet end (19) integral with the central diabolo(11) and are connected via sealed connections (22) to fixed means (27)for supplying the auxiliary dilution fluid. It is important that thecharacteristic run-off (12) be arranged in the vicinity of the smallestcross-section of the central convergent body (11) and preferably on thispoint, an inlet radially remote from the axis of the chamber 1, in orderto satisfactorily recover the entire light fraction.

The introduction of washing water minimizes, in the case of paper pulps,the losses of fibers which tend to concentrate in the region of the wallwith the heavy contaminants.

In the advantageous embodiment of the device of FIG. 2, the unit (18,25)for continuous evacuation of the heavy fraction is associated withdevices (26,27) for continuous ejection of washing water which use thespace (26) situated between the outlet end (19) linked to thediabolo-shaped central body (11) and the outlet flange of the chamber(1) of the apparatus. In a simplified embodiment, the same devices(18,25) may be used alternately for the discontinuous injection of waterfor washing the heavy fraction and for discontinuous extraction of theheavy contaminants, the extraction phase being advantageously very shortcompared to the washing phase, in order to minimize the heavy-fractionlosses.

FIG. 3 shows in schematic form and in longitudinal cross-section adevice particularly suited to the cleaning of paper suspensions. Theinner wall of the chamber (1) is cylindrical. The characteristicdiabolo-shaped convergent central body (11) comprises:

a first frustoconical portion (30), tapered towards the outlet (7),occupying more than half the distance between the inlet (6) and theoutlet (7); for ease of manufacture and mounting, this frustoconicalportion (30) is fixed at its wide part (31) to the feed end (32) with acylindrical shape and having the oblique channels for injection of thepaper pulp; the distance D between the inner wall (50) of the chamber(1) and the wall (51) of the central body (30) thus increases uniformlyfrom the inlet (6) towards the outlet (7);

a second cylindrical portion (33) shrunk (34) onto the tapered end ofthe first portion (30), in order to define a zone with a smallercross-section and having at the periphery thereof orifices (35,36,37)and the inner wall (38) of which (see FIG. 4) has radial fins(40,41,42); the orifice (35-37) and fin (40-42) unit forms a run-offunit or radial passage means similar to (12); consequently, aspreviously (12), the run-off takes place at the low point of the centralbody (30);

a third frustoconical portion (45), but with a conicity which isopposite to, (30) integral at (46) with the cylindrical portion (33) andwhich has an axial duct (47) similar to (13), associated with therun-off unit (35-37, 40-42) and intended to extract the light fractionfrom the suspension.

In a practical embodiment, the cylindrical chamber (1) has an internaldiameter of 0.75 m for a length of 2.5 m. The cylindrical inlet portion(32) has a diameter of 0.62 m for a length of 0.2 m. The firstfrustoconical inlet portion (30) has a length of 1.7 m for a diameterwhich decreases gradually from 0.6 to 0.36 m. The cylindrical run-offsection (33) has a length of 0.2 m for a diameter of 0.36 m. The thirdfrustoconical outlet portion (45) has a length of 0.4 m with a diameterwhich increases from 0.45 to 0.55 m. Finally, the orifices (35,36) havea diameter of 0.05 m and the axial duct (47) has a diameter of 0.05 m.

Such a cleaner device according to FIGS. 3 and 4 is able to handlethroughputs of the order of five hundred cubic meters per hour and more.In the case where the suspension treated is a paper pulp suspension, thefiber consistency of which is of the order of 0 to 3%, and preferably ofthe order of 1.5%, the efficiency of this cleaner is comprised between90 and 99%, with a fiber loss rate of less than 0.5%. Moreover, theenergy consumption is considerably smaller compared to that of a plantcomprising two conventional cleaners in parallel (21 kw compared to 2×17kw), a saving to which a saving in pumping energy of 12 kw must beadded, i.e. a total of 21 kw compared to 46 kw for a nominal throughputof 450 m³ /hour. This considerable reduction is due to the increase inthe capacity of the apparatus and to the fact that it is no longernecessary to provide a counterpressure at the outlet of the apparatus.

Furthermore, because of the presence of the central body of revolution,in particular in a diabolo shape, which prevents the formation of theair core and because of the general symmetry of the device in rotation,the detrimental vibrations are eliminated.

The separating device of the invention has numerous advantages comparedto those known hitherto, in particular that described in the documentEP-B-0,037,347 of the Applicant mentioned in the preamble. There may bementioned:

the possibility of increasing the diameter of the chamber, in otherwords its volume, and therefore the production of treated substancesand, with equivalent efficiency, the specific productivity;

for the same quantity of treated substance, the possibility of reducingthe investment cost;

the reduction in the consumption of energy, by reducing the specificapparatus-driving and pumping powers, because of the reduction in thecounterpressure;

the substantial reduction in detrimental vibrations, which improves thelifespan of the mechanical elements (bearings, mountings, joints . . .).

Consequently, this device may be used successfully for the treatment andcleaning of various suspensions, such as for example suspensions ofvarious paper pulps, waste water or polluted water, water/petroleumsuspensions, etc.

We claim:
 1. A device for separating particles in a liquid, in which thesuspension to be cleaned is supplied to a chamber of revolution (1)rotating about a longitudinal axis (2), of the typecomprising:suspension supply means including first fixed means (5) forsupplying the suspension, arranged along the longitudinal axis (2) of achamber of revolution (1), having first means (6) for deviating thesuspension current towards the periphery of the chamber (1); means fordriving said chamber (1) in rotation about its longitudinal axis (2);second fixed means (9,10) for discharging the cleaned suspension anddifferent separated fractions, arranged along the longitudinal axis (2)of said chamber (1), having second deviating means (7,8), a means (13)for discharging a lightest component being arranged on the longitudinalaxis of rotation (2); and said second deviating means (7,8) providedupstream of the second fixed means (9,10) intercepting most of thethroughput of the suspension in the region of the periphery of thechamber (1), then deviating it towards the longitudinal axis of rotation(2) so as to recover most of the kinetic energy of rotation; said secondfixed means (9,10) being situated at the opposite end to that of thechamber (1) from the supply means (5,6) and being arranged at theperiphery of said chamber (1); a central body (11) of revolution beingarranged inside the chamber, along the longitudinal axis of rotation ofsaid chamber (1), between the first fixed means (5) supplying thesuspension and the second fixed means (9-10) discharging said cleanedsuspension, said central body of revolution (11):being mounted forrotation about its axis and having a general diabolo shape including aportion, which, from the inlet means (5,6), converges towards the outletmeans (7-10) terminating in a smallest cross-section; and wherein aradial passage means (12, 33-42) is arranged in the vicinity of thesmallest cross-section of said central body of revolution (11) has aninlet radially remote from said axis of rotation and is connected to anaxial outlet duct (13, 47) whereby said radial passage means (12, 33-42)provided in the general diabolo-shaped central body of revolutionconverts the residual energy of the vortex dynamic and static pressuresinto static pressure which avoids the counterpressure on the outlet sideand therefore enables the inlet pressure to be correspondingly reducedresulting in an appreciable saving in energy.
 2. The device as claimedin claim 1, wherein the chamber has an inner wall; the central body hasa wall; and further a gap D between the inner wall (50) of the chamber(1) and the wall (51) of the central body (11,30) increases graduallyfrom the inlet (5,6) towards the radial passage means (12, 33-42). 3.The device as claimed in claim 1, wherein the general diabolo-shapedcentral body of revolution (11) comprises three distinct portions,namely:a first frustoconical portion (30), tapered towards the outlet(7); a second cylindrical portion (33) connected to the first portion(30), having at its periphery, orifices (35-37) open to the chamber andthe radial passage means (40-42); a third portion (45), alsofrustoconical, but with a conicity which is opposite to that of thefirst portion (30), connected to the second cylindrical portion (33) andhaving an axial duct (47) associated with the radial passage means forextracting a light fraction.
 4. The device as claimed in claim 3,wherein the radial passage means consist of circumferentially spacedradial fins (40-42) internally of said cylindrical portion (33) adjacentsaid peripheral orifices (35-37) within the second cylindrical portion(33) and connected to the axial duct (47).
 5. The device as claimed inclaim 1, wherein the central convergent body has an inlet and an outletend; further the inlet and outlet ends are integral with the chamber (1)and are driven in rotation by a single motor at the same speed as thespeed of rotation of said chamber (1).
 6. The device as claimed in claim1, wherein the central convergent body (11) is driven in rotation at aspeed which is different from that of the chamber (1), but is integralwith at least one of the inlet (6) and outlet (7,8) ends of the chamber(1).
 7. The device as claimed in claim 6, wherein the generaldiabolo-shaped central body (11) has on its outer periphery of body (11)fins (14) which are equidistant circumferentially and arranged along ageneratrix.
 8. The device as claimed in claim 1, wherein said radialpassage means comprise at least one fin extending generally radiallyfrom said inlet radially remote from said axis of rotation towards saidaxial outlet duct (13,47).